1. Field of the Invention
This invention relates to an ink-jet recording head and a process for its formation; the ink-jet recording head being an ink-jet recording head comprising a plate member in which a plurality of pressure chambers partitioned with sidewalls are formed in the form of grooves and one side surface of which is caused to vibrate by a piezoelectric device to thereby control the pressure of an ink held in the pressure chambers and eject the ink from nozzles communicating with the pressure chambers.
2. Description of the Related Art
In conventional ink-jet recording heads, as shown in FIG. 10A, to a cavity plate 103 on one side surface of which pressure chambers (cavities) 101 are formed in the form of grooves, a plate material 105 is joined with an adhesive or the like on the one side surface where the pressure chambers open, to close the pressure chambers 101, and vibrating plates 107 and piezoelectric devices 109 are arranged on the plate material 105. Then, a drive voltage is applied to electrodes 111 and 113 provided to the piezoelectric devices 109, to thereby cause the piezoelectric devices 109 to deform and, concurrently therewith, the plate material 105 closing the pressure chambers 101 to deform, so that the pressure of ink in the pressure chambers 101 can be controlled to eject the ink outward from nozzles communicating with the pressure chambers 101.
In such a ink-jet recording head, usually a plurality of pressure chambers 101 are provided and the ink is ejected from the nozzles communicating with the pressure chambers 101, where it is important from the viewpoint of print quality that their ejection performance is uniform.
Now, the pressure chambers 101 are closed by joining the plate material 105 to the cavity plate 103 at the top edge faces 117 of the sidewalls that partition the pressure chambers 101. Thus, originally independent materials are joined to each other in respect of the cavity plate 103 forming the pressure chambers 101 and the plate material 105 deformed by the piezoelectric devices 109. Hence, the state of joining between them is greatly concerned with the deformation properties of the plate material 105, and the uniformity of accuracy at the joints affects the uniformity of ejection performance of the nozzles.
In order to uniform the accuracy at the joints, the top edge faces 117 of the sidewalls 115 and the plate material 105 side are required to have a high flatness. They are also required to be uniformly joined at the joints when joined with an adhesive or the like.
However, it is difficult to achieve a high flatness and uniform joining at the all joints, and any slightly non-uniform flatness or joining may cause a delicate change in the deformation properties of the plate material 105, vibrating plates 107 and piezoelectric devices 109 which are supported at the top edge faces 117 of the sidewalls 115, making it difficult to impart uniform ejection performance to all nozzles.
As also shown in FIG. 10B, in order to double resolution, one may have an idea that pressure chambers 201 are formed on both sides of a cavity plate 203 in a alternately half-pitch shifted state, and laminates of piezoelectric devices 209 and vibrating plates 207, respectively formed on plate materials 205, are joined in such a way that their positions are in agreement with the positions of the open areas of the pressure chambers 201, and thus the nozzles can be provided in a higher density. Since, however, the above problem also arises on the both sides, the problem of the non-uniformity in flatness and joining becomes more serious, bringing about the problem that it is difficult to make the nozzle density higher.
An object of the present invention is to provide an ink-jet recording head that can prevent the deformation properties of plate materials, cavity plates and piezoelectric devices from being affected by the non-uniform flatness and joining for each sidewall and can impart uniform ejection performance to all nozzles, and a process for forming such an ink-jet recording head.
To achieve the above object, the present invention provides an ink-jet recording head comprising a plate member in which a plurality of pressure chambers partitioned with sidewalls are formed in the form of grooves and one side of which is caused to vibrate by a piezoelectric device to thereby control the pressure of an ink held in the pressure chambers and eject the ink from nozzles communicating with the pressure chambers; wherein a sheet type piezoelectric device provided with electrodes and having been polarized is laminated to the plate member on the side opposite to the pressure chambers-formed side.
The present invention also provides a process for forming the ink-jet recording head as above; the process comprising the steps of;
forming an electrode on the surface of an unbaked sheet type piezoelectric device;
joining the sheet type piezoelectric device to the plate member on its one side, made of a material having a nature similar or identical to the sheet type piezoelectric device, to form a laminate;
baking the laminate, and after the baking;
forming pressure chambers in the form of grooves on the surface of the laminate on the plate member side;
covering the pressure chambers with a sheet-like cover member; and
before or after the covering with the sheet-like cover member, subjecting the sheet type piezoelectric device to polarization.
This and other objects, features and advantages of the present invention are described in or will become apparent from the following description.
In the ink-jet recording head of the present invention, a sheet type piezoelectric device provided with electrodes and having been polarized is laminated to the plate member on the side opposite to the pressure chambers-formed side. More specifically, the sheet type piezoelectric device is laminated to the plate member not on the open side of the pressure chambers but on its external surface on the side opposite thereto. This lamination can be achieved by, e.g., a method in which the sheet type piezoelectric device is joined with an adhesive to a plate member in which grooves for the pressure chambers have been made, or a method in which an unbaked sheet type piezoelectric device and an unbaked plate member with the grooves are brought into close contact by vacuum pressing or the like followed by baking to form the pressure chambers.
Accordingly, since the sheet type piezoelectric device is not joined on the open side of the pressure chambers of the plate member, it follows that the device is not joined to the top edge faces of the sidewalls partitioning the pressure chambers and is laminated to the external surface on the opposite-side continuous single surface of the plate member. Thus, for both the sheet type piezoelectric device side and the plate member side, the uniformity concerning flatness and joining may be achieved on the single surface, so that a lamination that is uniform over the all pressure chambers can be achieved with ease and hence an ejection performance that is uniform over the all nozzles can be attained.
The other side of the plate member, the open side of the pressure chambers, may be covered with a sheet-like cover member. Even if this sheet-like cover member is joined a little non-uniformly, there can not be any effect that may come into question on the ejection performance, because any deformation does not take place on the side of the sheet-like cover member.
As the direction of polarization, the sheet type piezoelectric device may be polarized, e.g., in its thickness direction. In this instance, the electrodes may be so disposed that the direction of electric fields is identical with or reverse to the direction of polarization, i.e., in what is called the unimorph type formation. For example, the electrodes may be so disposed that they are formed on both sides of the sheet type piezoelectric device, where,,of the electrodes, ones on the side of which the piezoelectric device is laminated to the plate member or on the side opposite thereto are provided for each pressure chamber. An electrode on the side opposite to the electrodes provided for each pressure chamber may be formed as an electrode common to the all pressure chambers.
Upon application of a drive voltage to such electrodes, when, e.g., the electric fields and polarization are in the same direction, the sheet type piezoelectric device held between the electrodes partly shrinks in the direction perpendicular to the direction of polarization. Here, the plate member standing laminated to the sheet type piezoelectric device does not shrink, and hence the sheet type piezoelectric device and the plate member partly bend to become convex on the plate member side, i.e., on the side of a pressure chamber. This causes a decrease in volume of the pressure chamber to cause an increase in pressure of the ink, so that the ink is ejected from the corresponding nozzle. Once the application of the drive voltage is stopped, the bent portion of the sheet type piezoelectric device and plate member returns to the original state and the volume of the pressure chamber returns to the original volume, so that the ink is sucked therein from the feeding side.
On the other hand, when, e.g.,. the electric fields and polarization are in reverse direction, the sheet type piezoelectric device held between the electrodes partly extends in the direction perpendicular to the direction of polarization. Here, the plate member standing laminated to the sheet type piezoelectric device does not extend, and hence the sheet type piezoelectric device and the plate member partly bend to become concave on the plate member side, i.e., on the side of a pressure chamber. This causes an increase in volume of the pressure chamber, so that the ink is sucked therein from the feeding side. Once the application of the drive voltage is stopped, the extended portion of the sheet type piezoelectric device and plate member returns to the original state and the volume of the pressure chamber returns to the original volume, so that the ink is ejected from the corresponding nozzle. In this way, these can function as an ink-jet recording head.
The electrodes may also be so disposed that the direction of electric fields and the direction of polarization cross each other, i.e., in what is called the shearing mode type formation. They may cross, e.g., at right angles or at substantially right angles. In this instance, the electrodes may be so disposed that they are formed on one side or both sides of the sheet type piezoelectric device, and they are respectively provided at the positions corresponding to the pressure chambers and at the positions corresponding to the boundaries between adjoining pressure chambers.
Upon application of a drive voltage to such electrodes, the sheet type piezoelectric device held between the electrodes partly undergoes thickness slippage to deform. In accordance with this deformation, the plate member partly deforms to become convex or concave on the side of a pressure chamber. This causes a change in volume of the pressure chamber, so that the ink is ejected from the corresponding nozzle or sucked in the pressure chambers from the feeding side. Once the application of the drive voltage is stopped, the deformed portion of the sheet type piezoelectric device and plate member returns to the original state and the volume of the pressure chamber returns to the original volume, so that the ink is sucked therein from the feeding side or ejected from the corresponding nozzle. In this way, these can function as an ink-jet recording head.
The electrodes may still also be disposed at the position that produces both the part where the direction of electric fields and the direction of polarization cross each other and the part where the former is identical with or reverse to the latter, i.e., using the unimorph type formation and the shearing mode type formation in combination. In this instance, the electrodes may be so disposed that they are formed on both sides of the sheet type piezoelectric device, and they are respectively formed at the positions corresponding to the pressure chambers and at the positions corresponding to the boundaries between adjoining pressure chambers on one side, and an electrode common to the all pressure chambers is formed on the other side. Under such formation, upon application of a drive voltage to such electrodes, the action of the both unimorph type and shearing mode type causes a change in volume of the pressure chamber, so that the ink is ejected from the corresponding nozzle or sucked in from the feeding side. Once the application of the drive voltage is stopped, the deformed portion of the sheet type piezoelectric device and plate member returns to the original state and the volume of the pressure chamber returns to the original volume, so that the ink is sucked in from the feeding side or ejected from the corresponding nozzle. In this way, these can function as an ink-jet recording head.
Utilizing the characteristic features of the present invention as described above, the present invention may also be constituted as described below. That is, two sets of the ink-jet recording head of the present invention as described above may be formed into one unit by joining them on the sides of their respective sheet-like cover members. For example, the two ink-jet recording heads may be joined in the manner the positions of the pressure chambers are alternately half-pitch shifted, to form one ink-jet recording head. When they are joined in this way, the arrangement density of nozzles can be doubled and also the resolution can be doubled. Such an ink-jet recording head, even though its pressure chambers are doubled, can achieve uniform lamination in respect to the all pressure chambers with ease and can attain uniform ejection performance in the all nozzles.
The two ink-jet recording heads may be joined using one sheet of the sheet-like cover member in common. This can save the sheet-like cover member.
The ink-jet recording head of the present invention can be formed, e.g., by the process as already described.
It is a process for forming the ink-jet recording head comprising a plate member in which a plurality of pressure chambers partitioned with sidewalls are formed in the form of grooves and one side of which is caused to vibrate by a piezoelectric device to thereby control the pressure of an ink held in the pressure chambers and eject the ink from nozzles communicating with the pressure chambers, wherein a sheet type piezoelectric device provided with electrodes and having been polarized is laminated to said plate member on its surface on the side opposite to the side on which the pressure chambers are formed in the form of grooves, the process comprising the steps of:
forming an electrode on the surface of an unbaked sheet type piezoelectric device;
joining the sheet type piezoelectric device to a plate member on its one side, made of a material having a nature similar or identical to the sheet type piezoelectric device, to form a laminate;
baking the laminate, and after the baking;
forming pressure chambers on the surface of the plate member side of the laminate;
covering the pressure chambers with a sheet-like cover member; and
before or after the covering with the sheet-like cover member, subjecting the sheet type piezoelectric device to polarization.
Here, as the polarization, the sheet type piezoelectric device may be polarized, e.g., in its thickness direction. In this instance, the electrodes may be so formed that the direction of electric fields is identical with or reverse to the direction of polarization.. For example, the electrodes are formed on both sides of the sheet type piezoelectric device, and electrodes on the side the piezoelectric device is laminated to the plate member or on the side opposite thereto are provided for each pressure chamber. An electrode on the side opposite to the electrodes provided for each pressure chamber may be formed as an electrode common to the all pressure chambers.
The electrodes may also be so formed that the direction of electric fields and the direction of polarization cross each other. In this instance, the electrodes may be formed on one side or both sides of the sheet type piezoelectric device, and they are respectively provided at the positions corresponding to the pressure chambers and at the positions corresponding to the boundaries between adjoining pressure chambers.
The electrodes may still also be formed at the position that produces both the part where the direction of electric fields and the direction of polarization cross each other and the part where the former is identical with or reverse to the latter. In this instance, the electrodes may be formed on both sides of the sheet type piezoelectric device, and they are respectively formed at the positions corresponding to the pressure chambers and at the positions corresponding to the boundaries between adjoining pressure chambers on one side, and an electrode common to the all pressure chambers may be formed on the other side.
The pressure chambers can be formed on the surface of the plate member by shot blasting. The pressure chambers may also be formed by other cutting methods. The method such as shot blasting is preferred because it can form the pressure chambers without causing any strain in the plate member.
The ink-jet recording head constituted of the two ink-jet recording heads described above, formed into one unit by joining them on the sides of their respective sheet-like cover members can be produced, e.g., by a process as described below.
It is a process which comprises joining the laminate formed by the above ink-jet recording head formation process carried out up to the step before the joining of the sheet-like cover member, to the ink-jet recording head formed by the above ink-jet recording head formation process; the pressure chamber side of the former being joined to the sheet-like cover member side of the latter. They may be joined in the manner the positions of the pressure chambers are alternately half-pitch shifted.